(1) Field of the Invention
The present invention relates to a liquid storing device for storing a liquid such as ink used in, for example, an inkjet recording device or the like, a liquid storing method, and an inkjet recording device.
(2) Description of Related Art
As a simple and inexpensive means of recording images, image recording devices that use inkjet printing are known (hereinafter referred to as “inkjet recording device”). Inkjet recording devices record a desired image by ejecting droplets of ink from nozzles on a printhead onto a recording medium. The trend with such an inkjet recording device in recent years is to increase the size of the ink tank, so as to enable mass printing and continuous printing and to avoid the trouble of having to replace ink cartridges or the like. Another approach is to provide two main ink tanks as an ink tank and use them alternately so that printing is not interrupted midway.
However, the increase in volume of the ink tank has led to a problem that a larger amount of ink is left over. That is, since a large-volume ink tank has a large cross-sectional area itself, a large amount of ink may still be left over even though a liquid surface detection sensor detects a low level of stored ink. In order to detect the amount of remaining ink in the ink tank (main tank) correctly, an ink-counter tank (tank with an ink counter function), for example, has been employed, which is provided between the main tank and a supply tube that leads to the printhead, as a means of grasping how much ink is left inside the main tank more correctly. FIG. 1 is an explanatory diagram illustrating a schematic configuration of such an ink-counter tank. The ink-counter tank (tank with an ink counter function) here corresponds to the liquid storing device.
As shown in the drawing, the ink-counter tank 100 is connected to a supply pump via a supply tube 101. Ink stored in the main tank (not shown) is supplied by this supply pump through the supply tube 101. The ink-counter tank 100 is equipped with a liquid surface detection sensor (not shown) for detecting the amount of remaining ink from the level of the stored ink. A discharge tube 102 is provided at the bottom of the ink-counter tank 100 for allowing the ink to be supplied to an intermediate tank or the like. A leak sensor is also attached to the ink-counter tank 100 so that leakage of ink from the ink-counter tank 100 can be detected.
A supply port of the supply tube 101 to the ink-counter tank 100 is formed at the bottom of the ink-counter tank 100, i.e., located below the level of stored ink. This is because, if the supply port is provided in an upper part of the ink-counter tank 100, i.e., above the level of ink, the ink supplied may drop down and splash on the surface of the ink, which may cause an erroneous detection by the liquid surface detection sensor.
Sometimes, however, the amount of remaining ink grasped with the use of such an ink-counter tank 100 may still not be accurate enough. For example, air that starts to be supplied with the ink to the ink-counter tank 100 as the amount of ink left in the main tank is reduced may cause an erroneous detection by the liquid surface detection sensor. That is, when ink containing air or air bubbles is supplied from the supply tube 101, air bubbles are generated in the stored ink, since the supply port is provided below the level of the ink. Bubbles may also be formed on the ink surface, and the ink level may fluctuate. These may result in an erroneous detection by the liquid surface detection sensor.
To deal with this problem, a degassing structure for a liquid delivery tube disclosed in Japanese Unexamined Patent Publication 2010-22953 may be used, for example. The document discloses an invention relating to a degassing structure for a liquid delivery tube, wherein a main tube through which liquid flows is diverged upwards into a degassing tube by a midway branch joint for removing air bubbles from the liquid. The branch joint includes an supply port where an upstream-side main tube on the upstream side of the main tube is connected, an outlet port where a downstream-side main tube on the downstream side of the main tube is connected, and an upward-oriented degassing port where an upstream side of the degassing tube is connected. The outlet port is oriented diagonally downwards. By adopting such a structure, allegedly, when a liquid containing air bubbles flows from upstream, the air bubbles in the liquid float up by buoyancy and flow into the degassing tube through the degassing port that diverges upwards. Even when the liquid containing air bubbles flows out the degassing port of the branch joint (branch part) and flows into the outlet port, allegedly, the air bubbles in the liquid float up by buoyancy, move along the top surface of the downwardly diagonal outlet port, and flow into the degassing port. However, it is difficult to completely remove air bubbles from the liquid even with such a method, since the liquid containing air bubbles can still flow out into the main tube.
Another possibility is to use a degassing method for a liquid delivery tube disclosed in Japanese Unexamined Patent Publication 2010-22956, for example. According to this invention, there are provided an inlet-side main tube connected to the supply port of a branch joint, an outlet-side main tube connected to the outlet, an upward-oriented degassing tube connected to a diverging end, a first flow passage open/close unit provided in a part of the degassing tube, and an air bubble sensor located to face the inlet-side main tube. When the air bubble sensor detects air bubbles, the first flow passage opening/closing unit is opened before the bubbles reach the outlet-side main tube, so that the liquid containing air bubbles flowing from the inlet-side main tube toward the outlet-side main tube flows into the degassing tube. However, it is difficult to completely remove air bubbles from the liquid even with such a method, since the liquid containing air bubbles can still flow out into the main tube.